1. Field
The present application relates generally to the transmission of information over a distribution network, and more particularly, to methods and apparatus for reduction of a peak to average ratio for an OFDM transmit signal.
2. Background
Data networks, such as wireless communication networks, have to trade off between services customized for a single terminal and services provided to a large number of terminals. For example, the distribution of multimedia content to a large number of resource limited portable devices (subscribers) is a complicated problem. Therefore, it is very important for network administrators, content retailers, and service providers to have a way to distribute content and/or other network services in a fast and efficient manner and in such a way as to increase bandwidth utilization and power efficiency.
In current content delivery/media distribution systems, real time and non real time services are packed and delivered to devices on a network. For example, a communication network may utilize Orthogonal Frequency Division Multiplexing (OFDM) to provide communications between a network server and one or more mobile devices. In this technology, a stream of OFDM symbols forming a transmit waveform are packed with services to be delivered over the distribution network. Each symbol comprises a number of sub-carriers that are modulated by the data to be transmitted.
Typically, transmit waveforms need to meet specifications set by regulatory authorities. In order to meet selected spectrum specifications, the amplification of transmitted signals should not introduce any distortion. For example, a transmitter's power amplifier should operate linearly over the entire dynamic range of the transmit signal.
One measurement of a transmit waveform is referred to as the Peak-to-Average-Ratio (PAR). Generally, transmit waveforms having higher PAR levels require bigger power amplifiers which consume more power. One approach used to reduce the PAR levels of a transmit waveform is to clip the transmit waveform to ensure certain PAR characteristics. Unfortunately, this technique has the consequence of producing high out-of-band frequency components, which are undesirable.
Therefore, it would be advantageous to have a system that operates to reduce the PAR levels of a transmit waveform without producing high out-of-band frequency components and thereby overcoming the problems associated with high PAR levels.